1. Field of the Invention
The invention generally relates to an electrostatic discharge (ESD) protection device, and more particularly, to an ESD protection device with serially connected PNP transistors.
2. Description of Related Art
Electrostatic discharge (ESD) is a phenomenon of releasing electrostatic charges from non-conductive objects, and which may cause damage to semiconductors and other electronic components in an integrated circuit (IC). When a normal charged body (for example, a person walking on carpet, a machine for packing ICs, or an instrument for testing an IC) gets in contact with a chip, the charged body releases electrostatic discharge to the chip, and the transient power of the ESD may damage or maim ICs in the chip.
In order to prevent the damage caused by ESD to an IC, an ESD protection device is usually disposed in the IC. Generally speaking, there are many different designs of the ESD protection device. A commonly adopted technique to achieve the ESD protection purpose is by using two serially connected N-type transistors, wherein a fixed bias voltage is supplied to the gates of the two serially connected N-type transistors. However, the ESD protection effect provided by such a structure is often affected by process variation, and accordingly the reliability of the ESD protection device is reduced.